The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a semiconductor device which can reduce leaning (or tilting) of a patterned structure.
When performing a gate stack process using a tungsten (W) layer as an electrode including a barrier metal, a re-oxidation process is generally required to repair etch damage resulting from etching a polysilicon layer. Also, a method for capping the gate stack using substantially the same material as a nitride-based layer before performing a re-oxidation process has been widely used to prevent oxidation of a barrier metal and a tungsten layer during the re-oxidation process. Stress is generated in the gate stack when W2N or WN is formed by a reaction between the tungsten-based layer and a nitrogen (N) containing material.
For a dynamic random access memory (DRAM) device having a line width of 0.1 μm or less, an aspect ratio of a gate rapidly increases as a gate pitch decreases during a gate stack process. At this time, if bilateral symmetry of thermal stress values given to a gate stack is broken during a subsequent thermal process like a capping nitride layer formation, torque is generated in one direction, causing the gate stack structure to lean or tilt in that direction. This tilt becomes even greater as the gate pitch decreases. This is because an increased aspect ratio causes increased torque. The tilt of the gate structure may result in improperly formed self-aligned contacts, causing decreased yields.
FIG. 1 is a micrograph view of an undesirable formation generated by a short circuit between a gate and a landing plug contact due to a tilt of the gate structure. A gate tilting (see ‘L’) is generated when forming a capping nitride layer C. The tilt may cause a short circuit between the gate and the landing plug contact.
A tilting of this type may also occur during processes for forming bit lines and metal lines including a tungsten-based layer, e.g., a tungsten layer and a tungsten nitride layer.